1. Field of the Invention
The invention generally relates to bioabsorbable drug delivery devices and methods of making the same. More specifically, the invention relates to drug delivery devices comprised of bioabsorbable materials formed into desired geometries by different polymer processing methods.
2. Related Art
Intraluminal endovascular stents are well-known. Such stents are often used for repairing blood vessels narrowed or occluded by disease, for example, or for use within other body passageways or ducts. Typically the stent is percutaneously routed to a treatment site and expanded to maintain or restore the patency of the blood vessel or other passageway or duct within which the stent is placed. The stent may be a self-expanding stent comprised of materials that expand after insertion according to the body temperature of the patient, or the stent may be expandable by an outwardly directed radial force from a balloon, for example, whereby the force from the balloon is exerted on an inner surface of the stent to expand the stent towards an inner surface of the vessel or other passageway or duct within which the stent is placed. Ideally, once placed within the vessel, passageway or duct, the stent will conform to the contours and functions of the blood vessel, passageway or duct in which the stent is deployed.
Moreover, as in U.S. Pat. No. 5,464,450, stents are known to be comprised of biodegradable materials, whereby the main body of the stent degrades in a predictably controlled manner. Stents of this type may further comprise drugs or other biologically active agents that are contained within the biodegradable materials. Thus, the drugs or other agents are released as the biodegradable materials of the stent degrade.
Although such drug containing biodegradable stents, as described in U.S. Pat. No. 5,464,450, may be formed by mixing or solubilizing the drugs with the biodegradable polymer comprising the stent, by dispersing the drug into the polymer during extrusion of the polymer, or by coating the drug onto an already formed film or fiber, such stents typically include relatively small amounts of drugs. For example, U.S. Pat. No. 5,464,450 contemplates containing only up to 5% aspirin or heparin in its stent for delivery therefrom. Moreover, the profile of drugs delivered from such stents tend to concentrate the drugs at a primary region of the stent rather than delivering drugs more uniformly along a length of the stent. Lengthwise delivery of drugs from a stent could enhance treatment of a targeted site, disease or condition. Further, such stents as disclosed in U.S. Pat. No. 5,464,450 are often made without radiopaque markers. The omission of radiopaque markers inhibit the visualization and accurate placement of the stent by the medical practitioner. Further still, stents produced by melt-spinning a polymer into fibers containing drugs in accordance with U.S. Pat. No. 5,464,450 tend to stretch the fibers as monofilaments at temperatures of 500-200° C. This process suggests the drugs incorporated into the stents are stable at high temperatures. Because relatively few high temperature stable drugs exist, this limits polymer processing options significantly for stents or other drug delivery devices.
Polymers are often processed in melt conditions and at temperatures that may be higher than is conducive to the stability of the drugs or other agents to be incorporated into a bioabsorbable drug delivery device. Typical methods of preparing biodegradable polymeric drug delivery devices, such as stents, include fiber spinning, film or tube extrusion or injection molding. All of these methods tend to use processing temperatures that are higher than the melting temperature of the polymers. Moreover, most bioabsorbable polymers melt process at temperatures at which most drugs are not stable and tend to degrade.
Stents of different geometries are also known. For example, stents such as disclosed in U.S. Pat. No. 6,423,091 are known to comprise a helical pattern comprised of a tubular member having a plurality of longitudinal struts with opposed ends. Such helical patterned stents typically have adjacent struts connected to one another via the ends. The pitch, or angle, of the longitudinal struts as it wraps around the tubular stent in the helical configuration is typically limited, however, by the manner in which the longitudinal struts are made. Limiting the pitch or angle of the longitudinal struts of such helical stents can adversely affect the radial strength of such stents.
In view of the above, a need exists for systems and methods that form implantable bioabsorbable polymeric drug delivery devices with desired geometries or patterns, wherein the devices have increased and more effective drug delivery capacity and radiopacity. Further in view of the above, a need exists for systems and methods wherein degradation of the drugs incorporated into the devices during processing is minimized. Still further in view of the above, a need exists for systems and methods that form the bioabsorbable devices into geometries having improved radial strength and variable strut pitch capabilities and configurations, and having increased and more effective drug delivery capacity and radiopacity.